The present invention relates to techniques for use in the manufacture of printed wiring assemblies and more particularly to systems for cleaning rosin flux residues off of printed wiring assemblies.
Whenever integrated circuit chips or other components are mounted on printed wiring assemblies and electrical contact is made by soldering whether it be wave, vapor phase or hand soldering, substantial amounts of rosin flux and associated activators and decomposition products are left as contaminants on the wiring assembly. The removal of these rosins flux residues from the confined spaces on the printed wiring assemblies, and especially from the low clearance areas under surface mounted devices (SMDs), has been a troublesome problem. This problem has held back the greater use of leadless devices because of their lower component-to-substrate clearances.
A number of methods for removing rosin flux residues have been tried and have been partially successful. High pressure sprays of solvent material directed at low angles to individual parts mounted on the printed wiring assemblies have been found to be somewhat effective. However, heavy populations of parts in small areas and the unidirectional nature of such sprays make it difficult to concentrate the flow of spray and assure that all areas are sufficiently cleaned. In any event, total removal of flux is difficult to achieve with this technique and, furthermore, small parts and solder joints are sometimes damaged by high pressure spraying.
Rosin flux residues have also been removed from printed wiring assemblies by vapor degreasing methods. However, it has been found that extended cleaning times are necessary to remove flux residues from confined spaces such as the areas beneath SMDs and that board surfaces assembled parts and part markings are often attacked by degreasing solvents. Ultrasonic cleaning has been proposed as a method to remove rosin flux residues but is not currently used because there are reasons to believe that sensitive parts and solder joints may be damaged by ultrasonic energy.
It is therefore an object of the present invention to provide a method and apparatus for efficiently and effectively cleaning rosin flux residues from printed wiring assemblies and the confined spaces on such assemblies.
It is another object of the present invention to provide a method for cleaning rosin flux residues from printed wiring assemblies which does not risk damage to the chips, components, solder joints and other parts making up the wiring assemblies.
It is a further object of the present invention to provide a method for cleaning rosin flux residues from printed wiring assemblies which is efficient and effective yet is simple and economic to perform.